It is known to use a dynamo (e.g. an electric motor/generator) to decelerate a vehicle by way of regenerative braking. The electrical energy produced during regenerative braking is typically dumped into (i.e.—absorbed by) the vehicle's rechargeable battery by the battery charging system. However the charging voltage of charging system is generally fixed, and so the amount of deceleration provided by regenerative braking may not be sufficient to slow the vehicle at the desired deceleration rate. Also, when a vehicle is decelerating, for example coasting, some of the deceleration force comes from engine pumping losses. However, if it is desired to maximize the amount of electrical energy produced during regenerative braking, then is desirable to minimize the engine pumping losses.